Attempts are often made to control electric motor drives as efficiently as possible. This means at its simplest that at a given load torque the current drawn by the motor is minimized. This minimizes the resistive losses in the motor. The minimization of current would be an easy task if the machine were ideal. In practice, however, the magnetic saturation of the iron parts of the machine makes the search for an ideal operation point a demanding process. Due to the saturation effect, the inductances of the machine are not constant, but change as a function of the stator current. The fact that inductances change as a function of the stator current makes the optimization of the production of torque a difficult task, because in alternating current machines the inductances have an influence on the magnitude of torque.
In order to maximize the torque with a given stator current during the operation of the drive, the behavior of the inductances should be known as a function of current or flux. The inductance behavior is also important for the operation of control of synchronous reluctance machines, especially if the machine is controlled without a measured rotor speed and position. Such open-loop control methods estimate the rotor position by using a mathematical model of the machine. In connection with synchronous reluctance machines, the open-loop control does not operate correctly if the saturation of the inductances is not properly taken into account.
In known inductance identification procedures, the rotor has to be rotated. Due to this requirement, at least in some processes, the identification must be carried out before the machine is coupled to the process. Further, in the methods in which the rotor is rotated, the time for carrying out the identification is long. In some inductance identification procedures, the synchronous reluctance motor has to be loaded. The application of load torque to the machine to be identified can be cumbersome, especially if the machine is already at the facilities of the end user.